Spurious Indo-Pacific connections to internal Atlantic multidecadal variability introduced by the global temperature residual method

Here, the efficacy of the commonly-used "global temperature residual method" for isolating the internal component of AMV is investigated by means of model Large Ensembles where the truth is known a priori. In this method, local sea surface temperature variability associated with global-mean temperature (G) is removed via linear regression, and the residuals regressed upon the North Atlantic residual timeseries.

We show that this method introduces spurious connections over the Indo-Pacific due to the fact that G in any single realization includes both external and internal components: the latter dominated by influences from Pacific Decadal Variability independent of AMV. This methodological shortcoming can be overcome by using the forced component of G in the residual method applied to individual model realizations and to observations.